The present invention generally relates to control systems, and more specifically, but not exclusively, relates to a heating, ventilation and air conditioning (HVAC) diagnostic system that can be monitored remotely by telephone or over a computer network.
Commercial grade HVAC systems are used to control the temperature and air quality of buildings, such as in offices, hospitals and manufacturing plants. Although the reliability of such systems has improved, occasional operational failures may still arise. Even when a HVAC system appears to be outwardly operating properly, it may have an internal problem that causes it to waste energy. Many factors can make troubleshooting these systems rather difficult. For example, the complexity of the controls and other systems in HVAC systems can make troubleshooting difficult. In addition, HVAC systems are usually located in areas that are hard for service technicians to access such as on rooftops. Since technicians typically cover large service territories, a service technician may not be always available to troubleshoot sporadic problems with the HVAC system. To make the technician""s job even more difficult, the HVAC sensors that are used by the technician for diagnosing problems can be unreliable and sometimes can even be the source of the HVAC malfunction. Under certain circumstances the actions of the technicians, such as opening an access panel, can make diagnosis impossible by changing the operational characteristics of the system to a large extent so as to make data collection useless.
Therefoer, there has been a need for the ability to inexpensively and accurately diagnose problems with remotely located HVAC systems.
One form of the present invention is a unique method for sensing measurements in a HVAC system. Other forms of the invention include a unique method of diagnosing HVAC problems and a unique HVAC diagnostic system.
Another form concerns a method that includes calibrating a remote sensor interface by determining one or more calibration delay times for the remote sensor interface with a processor. A first signal is sent from the processor to the remote sensor interface. In response, a second signal is received at the processor from the remote sensor interface. A delay between the sending and receiving is timed with the processor. An output level of a sensor operatively coupled to the remote sensor interface is determined, which is a function of the delay and the calibration delay times.
A further form concerns a system that includes a sensor device operable to sense a reading from a machine and a processor that is operatively coupled to the sensor device. The processor is operable to send a first signal to the sensor device and to receive a second signal from the sensor device. The sensor device is operable to delay sending the second signal in proportion to the reading. The processor includes an internal clock operable to time a time delay between sending the first signal and receiving the second signal. The processor is operable to determine the reading from the sensor device based on the time delay.
In another form, a heating, ventilation and air conditioning unit includes a controller for controlling operation of the unit. A diagnostic device is operatively coupled to the unit, and the diagnostic device is operable to monitor status of the unit. The diagnostic device includes a processor operatively coupled to the controller, a clock operatively coupled to the processor, and one or more remote sensors attached to the unit. The remote sensors are operable to generate output voltages proportional to readings from the unit. One or more multiplexers are operatively coupled to the sensors and the processor to select one of the sensors to read. A voltage-controlled oscillator is operatively coupled to the multiplexers, and the voltage-controlled oscillator is operable to generate pulses at frequencies proportional to the output voltages from the sensors. A counter is operatively coupled to the voltage-controlled oscillator and the processor. The processor is operable to send one or more first signals to the counter. The counter is operable to send one or more second signals to the processor in response to the first signals after counting a predefined number of pulses from the voltage-controlled oscillator. The timer is operable to time delay times between sending the first signals and receiving the second signals at the processor. The processor is operable to determine the readings from the sensor devices based on the delay times. The diagnostic device is operable to determine the unit status of the unit based on the readings from the sensors and signals from the controller.
Another form concerns a method diagnosing an air treatment system with a fan. In the method, occupancy of a building is determined with a processor, and operational status of the fan is determined with the processor. The processor calculates an outdoor air fraction of the system and determines validity of the outdoor air fraction. The processor determines an outdoor air fraction status by comparing the outdoor air fraction to a required outdoor air fraction for the building. The processor determines current mode status by comparing the outdoor air fraction with current mode of operation of the system. The unit status of the system is based at least on the occupancy of the building, the operational status of the fan, the validity of the outdoor air fraction, the outdoor air fraction status, and the current mode status. Output is provided based at least in part on the unit status.
Another form concerns a system that includes means for calibrating a remote sensor interface by determining one or more calibration delay times for the remote sensor interface, means for sending a first signal to the remote sensor interface, means for receiving a second signal from the remote sensor interface in response to the first signal, and means for timing a delay time between the first and second signals. The delay time corresponds to a sensor reading. The system further includes means for determining the sensor reading based on the delay time and the calibration delay times.
Still yet another form of the present invention concerns a system that includes means for determining occupancy of a building. The building has an air treatment system with a fan. The system further includes means for determining operational status of the fan, means for calculating an outdoor air fraction of the system, means for determining validity of the outdoor air fraction, means for determining outdoor air fraction status by comparing the outdoor air fraction to a required outdoor air fraction for the building, and means for determining current mode status by comparing the outdoor air fraction with current mode of operation of the system. The unit status of the system is based at least on the occupancy of the building, operational status of the fan, the validity of the outdoor air fraction, the outdoor air fraction status, and the current mode status. The system includes means for providing output based at least in part on the unit status.